Readme.md

Statements

Code blocks

consists of zero or more expressions enclosed in curly brackets { and };
they can be nested within each other indefinitely.

Example

{
  var a = 1;
  {
    var b = a + 2;
    {
      var c = b * 3;
    }
  }
}

Convention

• Use end-of-line semicolons, although it is optional when you have one expression per line
• Indent any code placed within curly brackets
• Use curly brackets, although they are optional when you have a block of only one expression

The if statement

if (condition) statement1 else statement2

if (condition1) statement1 else if (condition2) statement2 else statement3

Convention

Use code blocks for control statements, even when it is only one expression.

if (test)
  console.log('hello!'); //valid, but error-prone and should be avoided

if (test) { //preferred
  alert(test);
}

The switch statement

switch (expression) {
  case value1: statement1; break;
  case value2: statement2; break;
  //...
  case valueN: statementN; break;
  default: statement
}

The step-by-step procedure for executing a switch statement is as follows:

1. evaluate the switch expression found in parentheses, remember it
2. move to the first case, compare its value with the one from step 1
3. if the comparison in step 2 returns true, execute the code in the case block
4. after the case block is executed, if there's a break statement at the end of it, exit the switch
5. if there's no break or step 2 returned false, move on to the next case block, repeat steps 2 to 5
6. if we're still here (we didn't exit in step 4), execute the code following the default statement.

Note

• the switch statement works with all data types (in many languages it works only with numbers)
• the case values need not be constants, they can be variables and even expressions
• the comparison of value is done using the identically equal operator, so no type coercion occurs

Note

The switch statement prevents writing something like this:

if (i == 25) {
  console.log("25");
} else if (i == 35) {
  console.log("35");
} else if (i == 45) {
  console.log("45");
} else {
  console.log("other");
}

The equivalent switch statement is as follows:

switch (i) {
  case 25: console.log("25"); break;
  case 35: console.log("35"); break;
  case 45: console.log("45"); break;
  default: console.log("other");
}

Tip

Put a break statement after each case to avoid having cases fall through into the next one;
if you need a case statement to fall through, include a comment indicating the intentional omission.

switch (i) {
  case 25: // falls through
  case 35: console.log("25 or 35"); break;
  case 45: console.log("45"); break;
  default: console.log("other");
}

The do-while statement

The do-while statement is a post-test loop:
the escape condition is evaluated only after the code inside the loop has been executed;
the body of the loop is always executed at least once before the expression is evaluated.

do {
  statement
} while (expression);

example

var i = 0;
do {
  i += 1;
} while (i < 10);

console.log(i); //10

The while statement

The while statement is a pre-test loop:
the escape condition is evaluated before the code inside the loop has been executed;
it is possible that the body of the loop is never executed.

while (expression) statement

Example

var i = 0;
while (i < 10) {
  i += 2;
}

The for statement

The for statement is a pre-test loop with code before entering the loop and post-loop code.

for (initialization; expression; post-loop-expression) statement

Note

The for loops can be nested within each other.

var s = '\n';
var n = 3;
var m = 3;

for (var i = 0; i < n; i++) {
  for (var j = 0; j < m; j++) {
    s += '* ';
  }
  s += '\n';
}

console.log(s);
"
* * *
* * *
* * *
"

Note

The initialization, control expression, and postloop expression are all optional.
You can create an infinite loop by omitting all three, like this:

for (;;) { //infinite loop
 doSomething();
}

Note

The for loop can be turns into a while loop including only the control expression:

var count = 10;
var i = 0;
for (; i < count; ) {
  console.log(i);
  i++;
}

The for in statement

The for in statement is a strict iterative statement used to enumerate the properties of an object.

for (property in expression) statement

Example

var obj = {a: 1, b: 2, c: 3};
var s = '';
for (var key in obj) {
  s += key + ' ';
}
console.log(s); //"a b c ";